Google revealed two months ago that it was working on spy-proof messages, and at the Black Hat security conference in Las Vegas on Thursday Yahoo announced that they were making it a joint effort.

Despite their bitter competition, the corporations have already given the go-ahead to their executives and engineers to speak to each other and hold regular meetings on the program, the Journal said.

Yahoo pointed out that the potential new system will only encrypt the content of a message and not the person who sent it or the date of the email or the subject line.

The move is a reflection of the two companies looking for new business plans in the wake of fugitive contractor Edward Snowden leaking thousands of classified documents from the NSA, revealing the agency's mass data and phone surveillance.

There has been increased demand for cyber-security since the NSA scandal broke last year, with privacy advocates demanding tech companies place more importance on preventing intrusion from government spies and hackers.

Until recently, Yahoo did not have a leading executive dedicated to information security while Google recently announced that that its encrypted websites are safer. Microsoft, meanwhile, recently won a battle to prevent the government getting data stored in Ireland, according to the Journal.

But Bruce Schneier, a cyber-security specialist and chief technology officer at Co3 Systems Inc., said all these measures will cause great upheaval in what he calls a "public-private surveillance partnership."

"What's going to happen when the FBI goes to Google or Yahoo and says, 'I want the email from this guy,' and Google or Yahoo says, 'We can't give it to you?'" Schneier said.

Microsoft has previously announced that it is working to incorporate encryption technologies into the service formerly known as Hotmail, the Journal said. There are more than 400 million active accounts in Hotmail and Microsoft's free email service Outlook.com.

Executives at Yahoo and Google, which have access to 535 million unique email users between them, say the encryption tool, which has in the past been difficult to use, will involve a feature in the software that allows consumers to simply turn it on.

Christopher Soghoian, a security and privacy researcher at the American Civil Liberties Union, said the two tech firms are hoping to make the encryption technology easier for the average person to use.

However, executives at both companies do not expect many users to employ the system when and if it is first introduced next year, the Journal added.